A capacitor that has much greater energy density and power per pound than electrostatic and electrolytic capacitors. Used in myriad electronic circuits as well as hybrid and electric cars, ultracapacitors are also called "supercapacitors."

With a life cycle of more than a million charges, ultracapacitors are ideal for applications that require frequent, fast charges and discharges, such as hybrid vehicles that are constantly braking and accelerating. However, since they have much less energy density than storage batteries, they do not serve as a long-term energy source.

Ultra Thin Separation Layer
The separation area between the positive and negative electrodes was reduced from millimeters in electrostatic capacitors to microns in electrolytic capacitors to nanometers in ultracapacitors. Thus, the ratio of surface area to separation layer in ultracapacitors is orders of magnitude greater than its predecessors. See capacitor.